Former NFL star Lawrence Phillips has been found dead in his prison cell.

The 40-year-old, who was drafted by the St. Louis Rams in the first round of the 1996 NFL draft, was serving time at Kern Valley State Prison in California at the time of his death for two separate incidents - assaulting a girlfriend and hitting three teenagers with his car.

It is believed his death was a suicide.

Phillips was also facing additional charges at the time of his death after being accused of murdering his cellmate last year, Damion Soward.

Tragedy: Lawrence Phillips (above in 1996) was found dead in his prison cell at Kern Valley State Prison in California

Troubled: Phillips was sentenced to a total of 31 years in prison in 2009 for driving his car into three teenagers and assaulting his girlfriend

USA Today reports that Phillips was charged with murder in September, and was possibly facing the death penalty if convicted.

The month his cellmate's death, Phillips wrote a letter to his mother in which he said; 'I feel myself very close to snapping. My anger grows daily as I have become fed up with prison.

'I feel my anger is near bursting and that will result in my death or the death of someone else.'

Phillips was born in Arkansas but moved to California as a child, spending much of his younger years in foster homes.

He went on to become a star running back at the University of Nebraska, where his incredible speed and return team work led to him being noticed right off the bat by scouts.

It was also in college when Phillips' run-ins with the law began, with the young man being charged with a series of offenses, most notably assaulting his girlfriend during his junior year.

Phillips was only suspended from the team, and returned in time for Nebraska to win their second championship in as many years.

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He decided not to stay on the team for his senior year and entered the NFL draft where he was picked sixth overall by the St. Louis Rams.

He would have likely gone higher but other teams said that his off-field antics had been a major issue for them and they did not want to take the risk given his history.

He was released from the Rams in his second season and then went to the Dolphins, who released him after just two games when he was charged with assaulting a woman at a nightclub.

He went to play in the European league in 1998, and return to the NFL in 1999, joining the San Francisco 49ers.

That team suspended him before he could even complete his first season due to his open contempt and disregard for the coaching staff.

He never returned to the NFL after that, and in 2005 was arrested after he drove his car into three teenagers following an argument during a pickup football game.

At the of his arrest he was also wanted for two assaults which he committed against a former girlfriend.

He was sent to prison in March 2006 and had been there ever since, first getting 10 years which had been decreased to seven for felony assault with a deadly weapon, and then later getting 25 years in 2009 for charges of assault with great bodily injury, false imprisonment, making a criminal threat, and auto theft for the incident with his former girlfriend.

Phillips then allegedly murdered his cellmate on April 11, 2015, was charged on September 1 and was awaiting trial.